At present, specified gaps remain between the building door/window hole and the additional frame or side frame in order to obtain more accurate installation of the additional frame or side frame of building door/window. For the above gaps, the means of manual filling and plastering is adopted after internal components are fixed, in order to complete later caulking and surface treatment, and for larger gaps, construction personnel generally fill them with broken bricks or other impurities at first and then adopts the method of manual caulking and plastering, such a construction method has the deficiencies of slow construction progress, poor caulking compactness of the gaps and poor reliability, poor caulking compactness and reliability become the source of water seepage and leakage as well as inferior heat preservation and insulation, in addition, the broken bricks or other impurities in the gaps have poor cementation firmness with cement mortar and poor compactness, and the broken bricks or other impurities filled in the gaps are also liable to cause the deformation of the additional frame or side frame of door/window, thus having a severe impact on construction quality as well as safety and service life of building door/window, and creating hidden troubles for the building envelope structure of building door/window.